Method for handling radio bearer messages during reset and reestablishment in a wireless system

ABSTRACT

A method of transmitting downlink data after re-establishment of a universal terrestrial radio access network (UTRAN) acknowledged mode (AM) radio link control (RLC) entity includes receiving a plurality of RLC service data units (SDUs) from a packet data convergence protocol (PDCP) layer of the UTRAN; dividing the received RLC SDUs into RLC protocol data units (PDUs) and transmitting the RLC PDUs to a user equipment (UE); receiving acknowledgments from the UE for received RLC PDUs; receiving a re-establishment request at a transmitting side of the AM RLC entity from upper layers of the UTRAN; discarding all RLC SDUs that have been fully transmitted to the UE before the re-establishment request is received; and discarding all RLC SDUs that have not been fully transmitted to the UE when the re-establishment request is received.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part (CIP) of application Ser. No.11/164,250, filed on Nov. 16, 2005 and now abandoned, entitled “Methodof Handling RLC SDUs During RLC Reset and RLC Re-establishment in a UMTSSystem,” the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods for handling messages afterreset and reestablishment in wireless systems, and more particularly, toa method for handling radio resource control (RRC) radio bearer 3 (RB3)messages after re-establishment due to SRNS relocation in anacknowledged mode (AM) radio link control (RLC) entity that belongs toRB3.

2. Description of the Prior Art

In a universal mobile telecommunications system (UMTS), a universalterrestrial radio access network (UTRAN) communicates with a pluralityof mobile stations, also referred to as user equipment (UE). FIG. 1 is adiagram illustrating network layers of the UMTS protocol. Layers of a UE10 and a UTRAN 20 are shown. Both the UE 10 and the UTRAN 20 areillustrated having the same network layers. Level 3 layers contain botha packet data convergence protocol (PDCP) layer and a radio resourcecontrol (RRC) layer. Level 2 layers contain both a radio link control(RLC) layer and a media access control (MAC) layer. Level 1 contains aphysical layer. These layers are all well known to those skilled in theart, and will only be described as they relate to the present invention.

The present invention primarily concerns interaction between the PDCPlayer and the RLC layer, as well as interaction between the RRC layerand the RLC layer. The terms service data unit (SDU) and protocol dataunit (PDU) are well known in the art. The terms PDU and SDU are relativewith respect to the current layer being described. An SDU is a piece ofinformation received from a layer above the current layer fortransmission using the service of the current layer. A PDU is a piece ofinformation processed by the current layer. Please refer to FIG. 2. FIG.2 is a diagram illustrating PDCP PDUs 30, 32 being segmented into RLCPDUs 34, 36, 38 according to the prior art. The RLC receives PDCP PDUsas RLC SDUs and segments the RLC SDUs into RLC PDUs. For simplicity,packet headers are ignored in this diagram. The size of each RLC PDU 34,36, 38 is configured by the UTRAN 20, whereas the size of each PDCP PDU30, 32 is not set by the UTRAN 20. As shown in FIG. 2, a first PDCP PDU30 is segmented to produce RLC PDUs 34 and 36 and part of RLC PDU 38.Since there is still room in the RLC PDU 38 for more data, part of thePDCP PDU 32 data is also added to the RLC PDU 38. This segmentationprocess continues for dividing all PDCP PDUs into RLC PDUs.

In acknowledged mode (AM) transmission and reception, each time an AMRLC entity sends a PDU, a corresponding acknowledgement should bereceived from the AM RLC entity receiving the PDU. For radio bearersthat are configured to support lossless SRNS relocation, when the SRNSrelocation is performed, the transmitting side of the AM RLC entity isre-established. Further, for radio bearers configured to supportlossless downlink RLC PDU size change, occasionally the UTRAN 20 willchange the size of the downlink RLC PDU segment size. In this case,upper layers will also request the transmitting side of the UTRAN AM RLCentity to be re-established. Please refer to FIG. 3. FIG. 3 illustratesa situation in which the UTRAN AM RLC entity is re-established. TheUTRAN PDCP entity submits PDCP data PDUs 40-43 with sequence numbers(SNs) equaling 77, 78, 79, and 80 to the UTRAN AM RLC entity. The UTRANAM RLC entity then begins transmitting the PDCP data PDUs to the UE 10.When the SRNS relocation is performed, or when the downlink RLC PDU sizeis changed by the UTRAN 20, the transmitting side of the UTRAN AM RLCentity is re-established. At this time, the PDCP Data PDUs 40, 41 withSNs=77 and 78 have been transmitted by the transmitting side of UTRAN AMRLC entity but have not been acknowledged positively. According to theprior art, when the transmitting side of the UTRAN AM RLC entity isre-established, the AM RLC entity discards all RLC SDUs that have beentransmitted completely in the transmitting side. This means that RLCSDUs containing data for the PDCP Data PDUs 40, 41 with SN=77 and 78 arediscarded. At this point the PDCP Data PDUs 42, 43 with SNs=79 and 80have not been transmitted by the transmitting side of UTRAN AM RLCentity. These PDCP Data PDUs 42, 43 are put in a buffer for latertransmission.

Due to the re-establishment, the AM RLC entity re-segments the SDUs thatwere not discarded into AM data (AMD) PDUs with the configured RLC PDUsize (which may be different from the size before the re-establishment)so an RLC SDU containing PDCP Data PDU 42 with SN=79 and an RLC PDUcontaining PDCP PDU 43 with SN=80 are re-segmented. If the PDCP entityin the UTRAN 20 has to trigger a PDCP SN synchronization procedure, itsubmits one PDCP SeqNum PDU 44 to lower layers. Because the smallestunacknowledged SN is 77, the PDCP entity submits a PDCP SeqNum PDU 44with SN=77 containing the same data as the PDCP Data PDU 40 with SN=77.PDCP Data PDUs 45, 46, 47 with SN=78, 79, and 80 are also submitted tothe AM RLC entity again.

Unfortunately, since the PDCP Data PDUs 42, 43 with SNs=79 and 80 werenot discarded during re-establishment, they were put in a buffer forlater transmission. That means when the UTRAN AM RLC entity latersubmits PDCP SeqNum PDU 44 with SN=77 and PDCP Data PDUs 45, 46, 47 withSN=78, 79, and 80, PDCP data PDUs with SN=79 and 80 are transmittedtwice. Not only does this waste radio resources by transmitting PDUstwice, it also disrupts the delivery sequence of the PDCP data PDUssince the SNs=79 and 80 are sent from the buffer before the SNs=77-80are sent after re-establishment.

Please continue to refer to FIG. 3. The same problem described abovethat applies to re-establishment also applies to RLC reset events.Consider again the situation for a radio bearer that is eitherconfigured to support the SRNS relocation or configured to supportlossless downlink RLC PDU size change. The UTRAN PDCP entity submitsPDCP data PDUs 40-43 with SNs equaling 77, 78, 79, and 80 to the UTRANAM RLC entity. The UTRAN AM RLC entity then begins transmitting the PDCPdata PDUs to the UE 10. If a condition of RLC reset is fulfilled, theRLC reset procedure is triggered. At this time, the PDCP Data PDUs 40,41 with SNs=77 and 78 have been transmitted by the transmitting side ofUTRAN AM RLC entity but have not been acknowledged positively. Accordingto the prior art, when the UTRAN AM RLC entity is reset, the AM RLCentity discards all RLC SDUs that have been transmitted completely inthe transmitting side. This means that RLC SDUs containing data for thePDCP Data PDUs 40, 41 with SN=77 and 78 are discarded. At this point thePDCP Data PDUs 42, 43 with SNs=79 and 80 have not been transmitted bythe transmitting side of UTRAN AM RLC entity. These PDCP Data PDUs 42,43 are put in a buffer for later transmission.

Next, the PDCP entity in the UTRAN 20 triggers a PDCP SN synchronizationprocedure by submitting one PDCP SeqNum PDU 44 to lower layers. Becausethe smallest unacknowledged SN is 77, the PDCP entity submits a PDCPSeqNum PDU 44 with SN=77 containing the same data as the PDCP Data PDU40 with SN=77. PDCP Data PDUs 45, 46, 47 with SN=78, 79, and 80 are alsosubmitted to the AM RLC entity again.

Unfortunately, no handling method is specified for the RLC SDUs thatwere not transmitted before the reset in the transmitting side of theUTRAN AM RLC entity. If the PDCP Data PDUs 42, 43 with SNs=79 and 80were not discarded during the reset, they were put in a buffer for latertransmission. That means when the UTRAN AM RLC entity later submits PDCPSeqNum PDU 44 with SN=77 and PDCP Data PDUs 45, 46, 47 with SN=78, 79,and 80, PDCP data PDUs with SN=79 and 80 are transmitted twice. Not onlydoes this waste radio resources by transmitting PDUs twice, it alsodisrupts the delivery sequence of the PDCP data PDUs since the SNs=79and 80 are sent from the buffer before the SNs=77-80 are sent after thereset.

Please refer to FIG. 4. FIG. 4 illustrates a situation in which theUTRAN AM RLC entity belonging to RB3 is re-established. Consider RRCsignaling radio bearer RB3. The RRC submits RB3 messages 1 and 2 50, 51to the RLC. When the RB3 RLC is re-established due to SRNS relocation,the RRC RB3 message 1 50 has been transmitted but is not positivelyacknowledged. RRC RB3 message 2 51 has not been transmitted. After RLCre-establishment, the RRC retransmits the RB3 messages 1 and 2 52, 53.However, the RB3 RLC also keeps the RRC RB3 message 2, and may keep theRRC RB3 message 1. Therefore, the RRC RB3 messages 1 and 2 areduplicated in the buffer, and will be transmitted twice. This causesunnecessary retransmissions, and wastes radio resources.

Likewise, FIG. 4 also illustrates a situation in which the UE AM RLCentity belonging to RB3 is re-established. Consider RRC signaling radiobearer RB3. The RRC submits RB3 messages 1 and 2 50, 51 to the RLC. Whenthe RB3 RLC is re-established due to SRNS relocation, the RRC RB3message 1 50 has been transmitted, but is not positively acknowledged.RRC RB3 message 2 51 has not been transmitted. After RLCre-establishment, the RRC retransmits the RB3 messages 1 and 2 52, 53.However, the RB3 RLC also keeps the RRC RB3 message 2, and may keep theRRC RB3 message 1. Therefore, the RRC RB3 messages 1 and 2 areduplicated in the buffer, and will be transmitted twice. This causesunnecessary retransmissions, and wastes radio resources.

The prior art also suffers from other problems because the properhandling for certain situations is not specified. For instance, thelossless function is not provided for uplink transmission in a UE PDCPentity for a radio bearer configured to support lossless DL RLC PDU sizechange. The handling for RLC SDUs that have not been transmittedcompletely before RLC re-establishment is not specified clearly in thespecification. Therefore, a bad design, such as discarding RLC SDUs thathave not been transmitted completely before the RLC re-establishment,will introduce transmission delays because the discarded RLC SDUs haveto be recovered by upper layer retransmission.

Similarly, the handling for RLC SDUs that have not been transmittedcompletely before RLC reset is not specified clearly in thespecification. Therefore, a bad design, such as discarding RLC SDUs thathave not been transmitted completely before the RLC reset, willintroduce transmission delays because the discarded RLC SDUs have to berecovered by upper layer retransmission.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide methodsfor transmitting downlink and uplink data after re-establishment andreset of a UTRAN AM RLC entity for solving the problems described above.

According to an embodiment of the present invention, a method oftransmitting downlink data after re-establishment of a universalterrestrial radio access network (UTRAN) acknowledged mode (AM) radiolink control (RLC) entity includes receiving a plurality of RLC servicedata units (SDUs) from a packet data convergence protocol (PDCP) layerof the UTRAN; dividing the received RLC SDUs into RLC protocol dataunits (PDUs) and transmitting the RLC PDUs to a user equipment (UE);receiving acknowledgments from the UE for received RLC PDUs; receiving are-establishment request at a transmitting side of the AM RLC entityfrom upper layers of the UTRAN; discarding all RLC SDUs that have beenfully transmitted to the UE before the re-establishment request isreceived; and discarding all RLC SDUs that have not been fullytransmitted to the UE when the re-establishment request is received.

According to another exemplary embodiment of the present invention, amethod of transmitting downlink data after reset of a UTRAN AM RLCentity includes receiving a plurality of RLC SDUs from a PDCP layer ofthe UTRAN; dividing the received RLC SDUs into RLC PDUs and transmittingthe RLC PDUs to a UE; receiving acknowledgments from the UE for receivedRLC PDUs; receiving a reset command at the AM RLC entity for resettingthe AM RLC entity; discarding all RLC SDUs that have been fullytransmitted to the UE before the reset occurs; and discarding all RLCSDUs that have not been fully transmitted to the UE when the resetoccurs.

According to yet another embodiment of the present invention, a methodof transmitting radio bearer messages after re-establishment of anacknowledged mode (AM) radio link control (RLC) entity comprisesreceiving a plurality of radio bearer messages from a radio resourcecontrol (RRC) layer, transmitting the radio bearer messages to a peerRLC entity, receiving acknowledgments from the peer RLC entity forreceived radio bearer messages, receiving a re-establishment request ata transmitting side of the AM RLC entity from upper layers, discardingall radio bearer messages that have been fully transmitted before there-establishment request is received, and discarding all radio bearermessages that have not been fully transmitted when the re-establishmentrequest is received.

According to another embodiment of the present invention, a method oftransmitting radio bearer messages after reset of an acknowledged mode(AM) radio link control (RLC) entity comprises receiving a plurality ofradio bearer messages from a radio resource control (RRC) layer,transmitting the radio bearer messages to a peer RLC entity, receivingacknowledgments from the peer RLC entity for received radio bearermessages, receiving a reset command at the AM RLC entity from the peerRLC entity for resetting the AM RLC entity, discarding all radio bearermessages that have been fully transmitted before the re-establishmentrequest is received, and discarding all radio bearer messages that havenot been fully transmitted when the re-establishment request isreceived.

According to yet another embodiment of the present invention, a methodof transmitting radio bearer messages after re-establishment of a userequipment (UE) acknowledged mode (AM) radio link control (RLC) entitycomprises receiving a plurality of radio bearer messages from a radioresource control (RRC) layer of the UE, transmitting the radio bearermessages to a universal terrestrial radio access network (UTRAN),receiving acknowledgments from the UTRAN for received radio bearermessages, receiving a re-establishment request at a transmitting side ofthe AM RLC entity from upper layers of the UE, discarding all radiobearer messages that have been fully transmitted to the UTRAN before there-establishment request is received, and discarding all radio bearermessages that have not been fully transmitted to the UTRAN when there-establishment request is received.

According to the present invention, a method of transmitting radiobearer messages after reset of a user equipment (UE) acknowledged mode(AM) radio link control (RLC) entity comprises receiving a plurality ofradio bearer messages from a radio resource control (RRC) layer of theUE, transmitting the radio bearer messages to a user universalterrestrial radio access network (UTRAN), receiving acknowledgments fromthe UTRAN for received radio bearer messages, receiving a reset commandat the AM RLC entity for resetting the AM RLC entity, discarding allradio bearer messages that have been fully transmitted to the UTRANbefore the reset occurs, and discarding all radio bearer messages thathave not been fully transmitted to the UTRAN when the reset occurs.

According to the present invention, a method of transmitting downlinkdata after re-establishment of a universal terrestrial radio accessnetwork (UTRAN) acknowledged mode (AM) radio link control (RLC) entitycomprises receiving a plurality of RLC service data units (SDUs) from apacket data convergence protocol (PDCP) layer of the UTRAN, dividing thereceived RLC SDUs into RLC protocol data units (PDUs) and transmittingthe RLC PDUs to a user equipment (UE), receiving acknowledgments fromthe UE for received RLC PDUs, receiving a re-establishment request at atransmitting side of the AM RLC entity from upper layers of the UTRAN,discarding all RLC SDUs that have been fully transmitted to the UEbefore the re-establishment request is received, and keeping all RLCSDUs that have not been fully transmitted to the UE when there-establishment request is received and retransmitting the RLC SDUsthat were not fully transmitted after the re-establishment of thetransmitting side of the AM RLC entity if the UTRAN AM RLC entity doesnot support lossless SRNS relocation and lossless downlink RLC PDU sizechanges.

According to the present invention, a method of transmitting downlinkdata after reset of a universal terrestrial radio access network (UTRAN)acknowledged mode (AM) radio link control (RLC) entity comprisesreceiving a plurality of RLC service data units (SDUs) from a packetdata convergence protocol (PDCP) layer of the UTRAN, dividing thereceived RLC SDUs into RLC protocol data units (PDUs) and transmittingthe RLC PDUs to a user equipment (UE), receiving acknowledgments fromthe UE for received RLC PDUs, receiving a reset command at the AM RLCentity for resetting the AM RLC entity, discarding all RLC SDUs thathave been fully transmitted to the UE before the reset occurs, andkeeping all RLC SDUs that have not been fully transmitted to the UE whenthe reset occurs and retransmitting the RLC SDUs that were not fullytransmitted after the AM RLC entity is reset if the UTRAN AM RLC entitydoes not support lossless SRNS relocation and lossless downlink RLC PDUsize changes.

It is an advantage of the present invention that resources are saved bynot retransmitting data twice and that transmission delays are reducedby not forcing discarded RLC SDUs to be recovered through upper layerretransmission.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating protocol layers between UE and UTRAN.

FIG. 2 is a diagram illustrating PDCP PDUs being segmented into RLC PDUsaccording to the prior art.

FIG. 3 illustrates a situation in which the UTRAN AM RLC entity isre-established.

FIG. 4 illustrates a situation in which the UE/UTRAN AM RLC entitybelonging to RB3 is re-established.

FIG. 5 illustrates a situation in which the UTRAN AM RLC entity isre-established according to the present invention.

FIG. 6 illustrates a situation in which the UE/UTRAN AM RLC entitybelonging to RB3 is re-established according to the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 5. FIG. 5 illustrates a situation in which theUTRAN AM RLC entity is re-established according to the presentinvention. The present invention method of handling the re-establishmentis an improvement upon the prior art method, and the same referencenumbers will be used in FIG. 5 and FIG. 3, and the same referencenumbers will be used in FIG. 6 and FIG. 4, for convenience.

The UTRAN PDCP entity submits PDCP data PDUs 40-43 with sequence numbers(SNs) equaling 77, 78, 79, and 80 to the UTRAN AM RLC entity. The UTRANAM RLC entity then begins transmitting the PDCP data PDUs to the UE 10.When the downlink RLC PDU size is changed by the UTRAN 20, or when theSRNS relocation is performed, the transmitting side of the UTRAN AM RLCentity is re-established. At this time, the PDCP Data PDUs 40, 41 withSNs=77 and 78 have been transmitted by the transmitting side of UTRAN AMRLC entity but have not been acknowledged positively. Like the priorart, the present invention method also has the AM RLC entity discard allRLC SDUs that have been transmitted completely in the transmitting sidewhen the transmitting side of the UTRAN AM RLC entity is re-established.Differing from the prior art, the present invention also discards theRLC SDUs that were not transmitted before the re-establishment in thetransmitting side of the UTRAN AM RLC entity. Therefore, RLC SDUscontaining data for the PDCP Data PDUs 40-43 with SN=77-80 arediscarded.

If the PDCP entity in the UTRAN 20 has to trigger a PDCP SNsynchronization procedure, it submits one PDCP SeqNum PDU 44 to lowerlayers. Because the smallest unacknowledged SN is 77, the PDCP entitysubmits a PDCP SeqNum PDU 44 with SN=77 containing the same data as thePDCP Data PDU 40 with SN=77. PDCP Data PDUs 45, 46, 47 with SN=78, 79,and 80 are also submitted to the AM RLC entity.

Since the RLC SDUs containing data for the PDCP Data PDUs 42, 43 withSN=79, 80 are discarded during re-establishment, they are not placed ina buffer for later transmission. Thus, the PDCP Data PDUs with SN=79 and80 are only transmitted to the UE 10 one time instead of two, and thein-sequence delivery is properly maintained in the UE AM RLC entity.

Please continue to refer to FIG. 5. The present invention handlingmethod that is applied to re-establishment can also be applied to RLCreset events. The UTRAN PDCP entity submits PDCP data PDUs 40-43 withSNs equaling 77, 78, 79, and 80 to the UTRAN AM RLC entity. The UTRAN AMRLC entity then begins transmitting the PDCP data PDUs to the UE 10. Ifa condition of RLC reset is fulfilled, the RLC reset procedure istriggered. This reset state can be triggered by either a RESET PDU or aRESET acknowledge (ACK) PDU. At this time, the PDCP Data PDUs 40, 41with SNs=77 and 78 have been transmitted by the transmitting side ofUTRAN AM RLC entity but have not been acknowledged positively. Like theprior art, the present invention method also has the AM RLC entitydiscard all RLC SDUs that have been transmitted completely in thetransmitting side when the transmitting side of the UTRAN AM RLC entityis reset. Differing from the prior art, the present invention alsodiscards the RLC SDUs that were not transmitted before the reset in theUTRAN AM RLC entity. Therefore, RLC SDUs containing data for the PDCPData PDUs 40-43 with SN=77-80 are discarded.

Next, the PDCP entity in the UTRAN 20 triggers a PDCP SN synchronizationprocedure by submitting one PDCP SeqNum PDU 44 to lower layers. Becausethe smallest unacknowledged SN is 77, the PDCP entity submits a PDCPSeqNum PDU 44 with SN=77 containing the same data as the PDCP Data PDU40 with SN=77. PDCP Data PDUs 45, 46, 47 with SN=78, 79, and 80 are alsosubmitted to the AM RLC entity.

Since the RLC SDUs containing data for the PDCP Data PDUs 42, 43 withSN=79, 80 are discarded during reset, they are not placed in a bufferfor later transmission. Thus, the PDCP Data PDUs with SN=79 and 80 areonly transmitted to the UE 10 one time instead of two, and thein-sequence delivery is properly maintained in the UE AM RLC entity.

Please refer to FIG. 6. FIG. 6 illustrates a situation in which theUTRAN AM RLC entity belonging to RB3 is re-established or resetaccording to the present invention. The UTRAN RRC entity submits RRC RB3messages 50, 51 to the UTRAN AM RLC entity. The UTRAN AM RLC entity thenbegins transmitting the RRC RB3 messages to the UE 10, i.e. a peerentity of the UTRAN AM RLC entity. When the RB3 RLC is re-establisheddue to SRNS relocation, or when the RB3 RLC is reset, triggered by aRESET PDU or a RESET ACK PDU, the transmitting side of the UTRAN AM RLCentity is re-established or reset, respectively. At this time, the RRCRB3 message 50 has been transmitted by the transmitting side of UTRAN AMRLC entity but has not been acknowledged positively. Like the prior art,the present invention method also has the AM RLC entity discard all RRCRB3 messages that have been transmitted completely in the transmittingside when the transmitting side of the UTRAN AM RLC entity isre-established or reset. Differing from the prior art, the presentinvention also discards the RRC RB3 messages that were not transmittedbefore the re-establishment or reset in the transmitting side of theUTRAN AM RLC entity. Therefore, the RRC RB3 message 2 51 is alsodiscarded.

Since the RRC RB3 messages are discarded during re-establishment orreset, they are not placed in a buffer for later transmission. Thus, theRRC RB3 messages are only transmitted to the UE 10 one time instead oftwo, and radio resources are not wasted in the UE and UTRAN.

Likewise, FIG. 6 further illustrates a situation in which the UE AM RLCentity belonging to RB3 is re-established or reset according to thepresent invention. The UE RRC entity submits RRC RB3 messages 50, 51 tothe UE AM RLC entity. The UE AM RLC entity then begins transmitting theRRC RB3 messages to the UTRAN 20, i.e. a peer entity of the UE AM RLCentity. When the RB3 RLC is re-established due to SRNS relocation, orwhen the RB3 RLC is reset, triggered either by a RESET PDU or a RESETACK PDU, the transmitting side of the UE AM RLC entity is re-establishedor reset, respectively. At this time, the RRC RB3 message 50 has beentransmitted by the transmitting side of UE AM RLC entity but has notbeen acknowledged positively. Like the prior art, the present inventionmethod also has the AM RLC entity discard all RRC RB3 messages that havebeen transmitted completely in the transmitting side when thetransmitting side of the UE AM RLC entity is re-established or reset.Differing from the prior art, the present invention also discards theRRC RB3 messages that were not transmitted before the re-establishmentor reset in the transmitting side of the UE AM RLC entity. Therefore,the RRC RB3 message 2 51 is also discarded.

Since the RRC RB3 messages are discarded during re-establishment orreset, they are not placed in a buffer for later transmission. Thus, theRRC RB3 messages are only transmitted to the UTRAN 20 one time insteadof two, and radio resources are not wasted in the UE and UTRAN.

The present invention also specifies a handling method for uplinktransmission in a UE PDCP entity for a radio bearer configured tosupport lossless DL RLC PDU size change. The handling for RLC SDUs thathave not been transmitted completely before RLC re-establishment isperformed as follows. The AM RLC entity in the UE 10 discards all RLCSDUs that have been transmitted completely before the RLCre-establishment. However, all of the RLC SDUs that have not beentransmitted completely before the RLC re-establishment are not discardedand are re-segmented into AMD PDUs by the UE 10 after the reset isperformed successfully. Therefore, transmission delays are reduced withthe present invention method since the RLC SDUs that were not beentransmitted completely before the RLC re-establishment do not have to berecovered through upper layer transmission if they were discarded.

The same handling method can also be applied to a reset applied to a UEPDCP entity performing uplink transmission for a radio bearer configuredto support lossless DL RLC PDU size change. That is, the AM RLC entityin the UE 10 discards all RLC SDUs that have been transmitted completelybefore the RLC reset. However, all of the RLC SDUs that have not beentransmitted completely before the RLC reset are not discarded and arere-segmented into AMD PDUs by the UE 10 after the reset is performedsuccessfully.

In summary, the present invention handling methods save resources by notretransmitting data twice and avoid transmission delays by not forcingdiscarded RLC SDUs to be recovered through upper layer retransmission.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A method of transmitting downlink data after re-establishment of auniversal terrestrial radio access network (UTRAN) acknowledged mode(AM) radio link control (RLC) entity, the method comprising: receiving aplurality of RLC service data units (SDUs) from a packet dataconvergence protocol (PDCP) layer of the UTRAN; dividing the receivedRLC SDUs into RLC protocol data units (PDUs) and transmitting the RLCPDUs to a user equipment (UE); receiving acknowledgments from the UE forreceived RLC PDUs; receiving a re-establishment request at atransmitting side of the AM RLC entity from upper layers of the UTRAN;discarding all RLC SDUs that have been fully transmitted to the UEbefore the re-establishment request is received; keeping all RLC SDUsthat have not been fully transmitted to the UE when the re-establishmentrequest is received and retransmitting the RLC SDUs that were not fullytransmitted after the re-establishment of the transmitting side of theAM RLC entity if the UTRAN AM RLC entity does not support losslessdownlink RLC PDU size changes; and discarding all RLC SDUs that have notbeen fully transmitted to the UE when the re-establishment request isreceived if the UTRAN RLC entity supports lossless downlink RLC PDU sizechanges.
 2. A method of transmitting downlink data after reset of auniversal terrestrial radio access network (UTRAN) acknowledged mode(AM) radio link control (RLC) entity, the method comprising: receiving aplurality of RLC service data units (SDUs) from a packet dataconvergence protocol (PDCP) layer of the UTRAN; dividing the receivedRLC SDUs into RLC protocol data units (PDUs) and transmitting the RLCPDUs to a user equipment (UE); receiving acknowledgments from the UE forreceived RLC PDUs; receiving a reset command at the AM RLC entity forresetting the AM RLC entity; discarding all RLC SDUs that have beenfully transmitted to the UE before the reset occurs; keeping all RLCSDUs that have not been fully transmitted to the UE when the resetoccurs and retransmitting the RLC SDUs that were not fully transmittedafter the AM RLC entity is reset if the UTRAN AM RLC entity does notsupport lossless downlink RLC PDU size changes; and discarding all RLCSDUs that have not been fully transmitted to the UE when the resetoccurs if the UTRAN RLC entity supports lossless downlink RLC PDU sizechanges.
 3. The method of claim 2, wherein the reset command is an RLCRESET PDU.
 4. The method of claim 2, wherein the reset command is an RLCRESET acknowledgement (ACK) PDU.